Abstract
The Monaco Monte Carlo treatment planning system uses three‐beam model components to achieve accuracy in dose calculation. These components include a virtual source model (VSM), transmission probability filters (TPFs), and an x‐ray voxel Monte Carlo (XVMC) engine to calculate the dose in the patient. The aim of this study was to assess the TPF component of the Monaco TPS and optimize the TPF parameters using measurements from an Elekta linear accelerator with an Agility™ multileaf collimator (MLC). The optimization began with all TPF parameters set to their default value. The function of each TPF parameter was characterized and a value was selected that best replicated measurements with the Agility™ MLC. Both vendor provided fields and a set of additional test fields were used to create a rigorous systematic process, which can be used to optimize the TPF parameters. It was found that adjustment of the TPF parameters based on this process resulted in improved point dose measurements and improved 3D gamma analysis pass rates with Octavius 4D. All plans calculated with the optimized beam model had a gamma pass rate of > 95% using criteria of 2% global dose/2 mm distance‐to‐agreement, while some plans calculated with the default beam model had pass rates as low as 88.4%. For measured point doses, the improvement was particularly noticeable in the low‐dose regions of the clinical plans. In these regions, the average difference from the planned dose reduced from 4.4 ± 4.5% to 0.9 ± 2.7% with a coverage factor (k = 2) using the optimized beam model. A step‐by‐step optimization guide is provided at the end of this study to assist in the optimization of the TPF parameters in the Monaco TPS. Although it is possible to achieve good clinical results by randomly selecting TPF parameter values, it is recommended that the optimization process outlined in this study is followed so that the transmission through the TPF is characterized appropriately.
Highlights
In modern radiotherapy, treatment planning systems (TPSs) are used to generate dose distributions with the aim of maximizing tumor control and minimizing normal tissue complications
To validate the transmission probability filters (TPFs) optimization, measured point doses and 3D dose matrices for a number of clinical intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were compared to those calculated in the TPS
Due to the many small beamlets created by the Monaco TPS in complex IMRT plans, it is important that the closed leaf gap on the linear accelerator is appropriately set and that the TPS correctly models this behavior
Summary
Treatment planning systems (TPSs) are used to generate dose distributions with the aim of maximizing tumor control and minimizing normal tissue complications. Traditional forward based treatment planning has been supplemented by inverse planning, which uses dose optimization techniques including intensity modulated radiotherapy (IMRT)[1] and volumetric modulated arc therapy (VMAT),[2,3] to satisfy user specified criteria. To achieve the appropriate target coverage and respect the dose constraint criteria for organs at risk, both IMRT and VMAT use many irregularly shaped fields defined by multileaf collimators (MLCs). Desirable MLC design characteristics include low intraleaf and interleaf transmission, a small tongue and groove effect, a small leaf width, accurate and fast leaf positioning, and most importantly, reproducibility. Reproducibility is paramount in an MLC system as this attribute allows for accurate characterization of the MLCs in the TPS, which in turn facilitates accurate IMRT and VMAT deliveries
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
